Earthing choking coil or voltage transformer for high voltages



Aug. 14,l 192s.

ET PFIFFNER EARTHING CHOKNG COIL 0R VOLTAGE TRANSFORMER FOR HIGHVOLTAGES Filed June 9, 1925 2 Sheets-Sheet ,i O l1-Ilm@ 4 ffl'unwm Ai211/ u @z2/o@ l Pf ffii/er ?7% Aug.14,192s. y' 1,680,910

E. PFIF'FNER EARTHING CHOKING COIL OR VOLTAGE i'IRANSFORMER I FOR HIGHVOLTAGESlv JIJ ff? el Patented Aug. 14, 1928.

UNITED STATES EMIL PFIFFNEB, OF FRYBOURG, SWITZERLAND.

EARTHING CHOKING COIL OR VOLTAGE TRANSFORMEB FOR HIGH VOLTAGES.

Application led .Tune 9. `19215. Serial No. 85,997.

This invention relates to improvements in earthing choking coils orvoltage transformers for high voltages and essentially consists in theparticular construction of a compound or cascade transformer, whichrenders possible not only the carrying-off of continuous current chargesof the network, but also the connection of measuring devices, such asvoltmeters and output-meters.

One mode of carr ing out the present 1n- Vention is illustrate by way ofexample on the accompanying sheets of drawings in which Figs. l and 2show a compound transformer in sectional elevation, the section beingtaken at 90 degrees with respect to one'another. A

Figs. 3, 4 and 5 illustrate diagrammatically detail views, and t l Fig.6 shows the magnetization-lines of the individual transformers of whichthe compound transformer is composed.

Figs. 1 and 2 illustrate a compound or cascade transformer composed ofthree superposed transformers 1, 2 and 3, each individual transformerbeing in the shape of a shell transformer provided with cores 4 andyokes 5. The cores 4 as well as the yokes v5 are furnished withadjustable air-gaps 6. The primary windings 7 and the secondary windings8a, 8", 8c, 8d, 8e and 8f, connected in series are disposed around thecores 4. Further a compensating windin 9, in the form of alongitudinally slotte copper cyl1nder, is located round the core, and an.insulating sleeve 10 is arranged between the said cylinder and theprimary and secondary windings. Copper-sheets 11 are arranged b etweenthe coils of the primary winding 7, 1n order to improve the carrying-offof heat, the copper-sheets extending through the fillin material l2 tothe inner wall of the porce ain casing 13. The ends of the coppersheets11 are turned up, in order to provide a better conduction of heat fromthe said copper-sheets to the inner wall of the porcelain casing 13. Theindividual porcelain casings of the compound transformer are connectedwith each other by means of the armature-rings 14 and 15 cemented to thecorresponding porcelain casings and screwed toetlier, the said ringsbeing also employed or electrically connecting the transformers 1, 2 and2, 3 respectively. A second electric connection is established by meansof a platespring 18 cooperating with hoods 16 and 17,

which are cemented centrally to the porcelain casings. The secondarywinding 8Z of the transformer 3 is employed for feeding the measuringdevices. In order to protect o0 this winding against static charges, thesame is connected with a grounded metallic coil member 19 and with thecast-iron support 20 of the transformer. A terminal 22 and an insulatedterminal 2l are attached to the o5 in Fig. 4. The winding 25 is a partof the 70 choking coil winding 24, 25 and is connected to the coil 8 ofthe next transformer. This connection serves for establishing a certainratio between the field of the choking coil andthe field of the firsttransformer. Fig.

3l shows an arrangement of the choking coil 2,4Lwithout the compensatingcoil. Also. this iron core is provided with an adjustable air-gap 27.The choking coil is not embedded in a filling material, but is airinsulated andA protected by a metallic hood 28, which carries a supplyterminal 29. In order to properly distribute the electrostaticfieldoutside the transformer, conducting rain covers 30 or tubular raincovers 30 are clamped 85 between the armature-rings 14 and 15.

For the operation as a voltage transformer it is of importance, that incase of an increase or drop of the primary voltage the terminal voltageof the secondary winding always is varied in proportion with thevariation of the primary voltage. According to the present inventionthis condition is satisfied in that the individual transformers areprovided with different magnetizationg5 The degree of saturation in theadrf" lines. mission transformer l is greater than in the transformer 2,and in the latter greater than in the transformer 3, this beingaccomplished by varying the cross-sectional areas of the iron in theindividual transformers and by providing adjustable air-gaps in themagnetic circuit of these transformers. The number of air-gaps of atransformer depends on the desired kind of cliaracteristic of thistransformer. A comparison between the magnetization-lines of the threetransformersis illustrated in Fig. 6 of the drawings. At an ordinaryworking voltage the decrease of voltage in the first transformer islarger thanin the last transformer owing t0 this distribution of field.In case the primary voltage is increasing the decrease of voltage ofthis transformer will be more rapid than corresponds to the increase ofthe primary voltage, in consequence of the smaller saturation of thetransformer 3. However owing to the greater primary voltage and theincreased charging rate called for by this, the decreases of voltagehave also mounted up in consequence of leakage and resistance, andtherefore the observation of the correct secondary voltage is renderedpossible.

A connection is employed to distribute in the desired manner the primaryhigh voltage to the individual transformers. In the diagrammatic Viewshown in Fig. 3 two successive transformers 1 and 2, and 2 and 3respectively are coupled with each other by the coils 8", 8 and 8, 8respectively. These coils form a part of the' beginning and end of theprimary winding 7 of each transformer. The connection of these coils 8,8, 81 and 8 is such, that the voltages induced in the same yby thealternating field of the transformers are eliminated if the fields arealike, e. g. of the same strength. In case a difference in the fieldsarises owing to the dissimilarity of the magnetic resistances, a currentpasses through the said coils, the said current supplying ampereturns tore-establish the field-similarity. But these windings alone and theprimary Winding would result in a considerable leakage. In order toavoid this, a compensating winding is arranged within each individualtransformer. In Fig. 3, the reference characters 31, 31, 31", 31, 31dand 31 designate these windings of the three transformers. Eachcompensating winding consists of two coils arranged at the ends of thecore. These coils are connected with each other in such a manner, thatin case of similarity of the fields at the end of each core no currentis passing. A short-circuit current is produced which effects anequaliza tion of field,'in case of dissimilarity in the field of a core,which is caused in consequence of leakage between the said windings 31and the winding 7. As shown in Fig. 5, a longitudinally slotted solidcylinder 9 of copper may be substituted for the winding 31. Thiscylinder prevents not only the leakage between the primary winding 7 andywindings 8, but also the leakage within the primary winding. The coppercylinder, disposed around the core, serves not only as a cover of thecore, but also acts as awinding and therefore has to consist of a wellconducting material. In case a pulsating magnetic iuX passes through thesaid cylinder, the tensions produced in the cylinder are eliminated onlyin case the strength of the magnetic field within the cylinder is alikeat all places. In case the field within the cylinder is not alike at allIn order to produce satisfactory condiy tions of insulation between theWinding and core, each iron core is brought to the medium potential ofthe corresponding de-y crease of voltage by means of the connection 32,32" and 32 attached to the middle of itsprimary winding. The end of theprimary winding of the last transformer 3 is grounded. In order to avoidthe coil 8', supplying the measuring instrument, from being charged withdangerous voltages by the static induction of the iron core, this coilis wound upon a conducting coil casing, which is connected with theearth connection of the transformer. In front of the first transformeris conductively mounted a choking coil 24 (Fig. 3), which protects thecompound transformer against jumping waves. This choking coil is notembedded in insulating material in order that it can be removedl easilyin case of defects. choking coil cany be usedl for correcting thetransformation ratio and any inaccuraciesof the voltage transformer. Forthis object the choking coil is provided with adjustable air-gaps in themagnetic circuit and with tapping places 33 (Fig. 4) for attachment tohe primary terminal 29. The tension of t e transformer can be reduced byproviding the choking coil with a larger number of windings. The tensionof the The loir

transformer and thus also of the measuring instrument can be increasedby reducing the number of windings of the choking coil. The correctnumber of windings is determined at the time of Calibrating thetransformer by connection to the convenient tapping place of the chokingcoil winding. The last turns 25 of the choking coil are connected withthe first compensation coil 82l of the first transformer for the purposeof magnetic connection or coupling.

1. A voltage transformer comprising in combination a plurality ofsections, each section having a magnetic circuit provided with an airgap, a primary winding on each section and a compensating winding oneach section connected in series with said primary winding, saidcompensating winding of each section being connected with the windingsof the adjacent sections.

2. A voltage transformer comprising in combination a plurality ofsections, each section having a. magnetic circuit provided with an airgap, a primary winding on each section, a compensating winding on eachsection connected in series with said primar winding, said compensatingwinding of eac section beingconnected with the windings of adjacentsections.

4. A transformer comprising' in combination, a plurality of sections,each section' having a magnetic circuit provided with an air gap, aplurality of coils in each section I magnetically'connecting saidmagnetic circuits and a slotted metallic cylinder arranged on the coreof each magnetic circuit.

5. A transformer comprising in combination a plurality of sections, eachsection having a magnetic circuit provided with an' air gap, a pluralityofcoils in each section magnetically connecting said magnetic circuits,a slotted metallic cylinder arranged on the core of each magneticcircuit, a. primary winding on each sectionk and an electric connectionbetween the core of each sectionvand the middle of said primary winding.

6. A transformer comprising in combination a plurality of sections, eachsection having a magnetic circuit provided 'with an air gap, a pluralityof coils in each section magnetically connecting said magnetic circuitsa slotted `metallic cylinder arranged on t e.

core of each magnetic circuit, av primary winding on each section, anelectric connection between the core of each section and the middle ofsaid winding, a measuring coil onthe last magneticcircuit, and agrounded conductive coil-casing on `which the said' measuring coil iswound. v

7. A voltagev transformer comprising `in combination a plurality ofsections, each secs tion having a magnetic circuit provided with an airgap, a primary Winding on eachsec'- tion, a compensating winding onleach sec-- tion connectedin series'with said primar winding, saidcompensating winding of eac section beingconnected with the windings ofthe adjacent sections, an electric connection between the core of eachsection and the yconductive coil-casinv an lair gap, a primary windingon each section, a compensating winding on each section connected inseries with said primar windin said compensating winding of eacsectioneing connected with the windings of thev adjacent sections, anelectric connection between the core of each section and the middle ofsaid primary winding, a grounded conductive coil-casing on the lastsection, a measuring coil wound on. said casin a choking coil disposedin front of all o the magnetic circuits and arranged in seriestherewith, and an adjustable air gap provided in the said choking coil.

A9. A voltage transformer comprising in combination a plurality ofsections, each section having a ma etic circuit provided with an airgap, a primary winding on each section, a compensatin winding on eachsec tion connected in series with said primar winding, said compensatingwinding of eac section being connected with the windings `of theadjacent sections, an electric connection between the core of eachsection andthe middle of said primary winding,a grounded conductivecoil-casin on'l the lastsection, a measurin .coil woun on said casing, achoking-coil disposed in front of all of the magnetic'. circuits andarranged in series therewith, an adjustable .air lgap provided in thesaid choking coil, and a plurality of taps on thewinding of said cholnngcoil.

. .10. A transformer comprising in -combination a pluralityof sections,each section having a ma etic circuit ofy different iron cross 'sectiona-area with respect to the other ma etic circuits, an air gap provided ineac' of the said circuits, and a-separate`insulting casing enclosingeach magnetic circui In testimony whereof I aix my signature.

EMIL PFIFFNER..

